Photodiode and CCD arrays are used for the location of peak irradiation. Such devices can offer good resolution but generally require an exhaustive search of the data from each detector element, which can limit the speed at which peaks are found. To obtain greater speed, it may be necessary to sacrifice position resolution. Such arrays do have an advantage in their ability to identify multiple peak locations.
Large area position detectors such as lateral effect photodiodes and quadrant detectors are useful for the location of a single peak in an input scene. Lateral effect devices provide high resolution through circuits which resolve the point of peak intensity within the large area in which lateral effect currents are measured.
Applications of devices which determine the location of peak intensities include pattern recognition systems (correlators), general peak position measurements such as that used in optical measurement systems and object tracking, optical detection for spectrometry, speckle interferometry, particle measurement and in establishing the correct position of optical elements and other machine parts during the manufacture of machines or during machine operation.
The ability to find the peak position within an area utilizing the photocell lateral effect was discussed by Walmark, "A New Semi-conductor Photocell using Lateral Photo Effect". Proceedings of the IRE 45,474 (1957). Walmark reports on a one dimensional lateral effect photocell to detect peak position within 100 angstroms and explains how the effect can be extended to a two dimensional photodetector.
U.S. Pat. No. 4,887,140 to Wang discloses a two dimensional lateral effect position sensitive device in which the area of the detector capable of providing a linear response to incident light is increased.
"An Array Type Position Sensitive Detector to Light Pattern Measurement" by Kawasaki et al., Sensors and Actuators A21-A23, 529 (1990) relates to an array of one dimensional lateral effect position sensors.
U.S. Pat. No. 5,059,814 to Mead et al. (1991) discloses a "winner take all" circuit for employment in a neural network computing system to indicate an input path of highest value. The circuit can also show the input of highest value within subgroups.
U.S. Pat. No. 4,945,242 to Berger et al. discloses an array of photodetectors wherein each pixel contains two photosensitive elements, one stacked on top of the other. The upper and lower photosensitive elements respond to different wavelengths of radiation making it possible to acquire two images simultaneously at different wavelengths.
U.S. Pat. No. 5,239,193 to Benton et al. discloses CMOS circuitry on the front surface of a well in combination with a photodiode on the well periphery.
As shown above the prior art reveals photosensors using the lateral effect with circuits that can locate the peak intensity within a pixel. Each of these peak intensity measurements within a pixel array can be compared to determine the location of peak intensity within the area of the array. To find the locations of multiple peaks, the prior art also shows that CCD arrays or photocell arrays are commonly used in combination with comparison circuits. It is the general object of this invention to provide high speed, high resolution location of multiple points of peak irradiation in the area of a photodetector array through minimizing the number of pixels while retaining high resolution.